1. Field of the Invention
The present invention relates to a sheet treating apparatus for transporting and stacking a sheet, in particular to an image forming apparatus, for example, a copying machine, a printer, or a facsimile apparatus, which is provided with a function for forming an image on a transfer material (recording medium) such as a sheet.
2. Related Background Art
FIG. 7 shows a schematic view of an image forming apparatus A1 in accordance with a conventional technique.
Conventionally, in an image forming apparatus employing the electrophotographic process, in general, a sheet is fed and transported into an apparatus main body, and a toner image is transferred onto the sheet and is fixed thereon by a fixing device T. When the sheet is to be delivered, it is transported by an FD upper roller 15 to be stacked on a delivery tray 19. Sheets 3 to be stacked on the delivery tray 19 are usually stacked from the bottom in the order of delivery so as to be aligned entirely along a tray shape of the delivery tray 19.
On the other hand, if the sheets 3 are delivered in a curled state, the sheets 3 are not aligned entirely along the tray shape but are stacked in a state in which a curled portion thereof partially deviates from the tray shape.
Therefore, a trailing edge of the sheets 3 stacked on the delivery tray 19 in the curled state covers and blocks a sheet delivery outlet of the apparatus main body and collides with a leading edge of a sheet to be subsequently delivered.
As a result, the succeeding sheet is bent at a corner thereof and is further bent in an accordion shape so that it cannot be delivered. This becomes a cause of jam, or of the succeeding sheet pushing out a trailing end of a sheet already stacked and further making the sheet fall off the tray.
Thus, conventionally, there is a structure for securing a sheet delivery outlet by adhering a Mylar (trademark) 10 to a top cover of a delivery portion with a pressure sensitive adhesive double coated tape as shown in FIG. 7 to hold down a trailing edge of sheets stacked on the delivery tray 19.
In this structure, the Mylar 10 with the pressure sensitive adhesive double coated tape adhered to one end thereof is adhered to a lower surface of the top cover situated above the FD upper roller, by pressing thereon a pressure sensitive adhesive double coated tape portion upward from below, whereby the other end of the Mylar 10 is positioned so as to serve as a sheet holding-down portion.
However, with this structure, since a sheet-passing portion of the Mylar 10 is worn and broken over the time of use, a long service-life cannot be expected of the Mylar 10.
In addition, the pressure sensitive adhesive double coated tape has to be used, which may come off depending upon the manner of adhesion, and for example, in the case in which the Mylar 10 itself is used in a bent state, an angle of abutment against a sheet with respect to an angle at which the sheet is delivered is not fixed. This tends to cause corner bending or jam.
Further, since the Mylar 10 is fixed to the lower surface of the top cover, a space for allowing adhesion of the Mylar 10 is required above the FD upper roller so that saving of space is difficult.